Derivatives of the Cardiac Tube

• First 3 weeks: primitive heart develops as a straight tube
  • Truncus arteriosus Truncus arteriosus Truncus arteriosus (TA) is a congenital heart defect characterized by the persistence of a common cardiac arterial trunk tract that fails to divide into the pulmonary artery and aorta during embryonic development. Truncus arteriosus is a rare congenital malformation with a high mortality rate within the 1st 5 weeks of life if not managed promptly. Truncus Arteriosus → ascending aorta and pulmonary trunk
  • Bulbus cordis
    • Proximal 3rd of bulbus cordis → muscular right ventricle
    • Conus cordis → smooth outflow portions of right and left ventricles
  • Endocardial cushion → atrial septum, membranous interventricular septum, atrioventricular (AV) valves, and semilunar valves
    • Derived from neural crest cells
    • Endocardial cushion defects: common in Down syndrome Down syndrome Down syndrome, or trisomy 21, is the most common chromosomal aberration and the most frequent genetic cause of developmental delay. Both boys and girls are affected and have characteristic craniofacial and musculoskeletal features, as well as multiple medical anomalies involving the cardiac, gastrointestinal, ocular, and auditory systems. Down Syndrome 
  • Posterior, subcardinal, supracardinal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins → inferior vena cava Inferior vena cava The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels ( IVC IVC The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels)
  • Primitive atrium → trabeculated parts of the left and right atria
  • Primitive pulmonary vein → smooth left atrium
  • Primitive ventricle → trabeculated parts of the left and right ventricles
  • Right common cardinal vein (RCCV) and right anterior cardinal vein (RACV) → superior vena cava Superior vena cava The venous trunk which returns blood from the head, neck, upper extremities and chest. Mediastinum and Great Vessels (SVC)
  • Left horn of sinus venosus → coronary sinus
  • Right horn of sinus venosus → posterior part of the right atrium (sinus venarum) with a relatively smooth surface
• Smooth portions are found in the areas where the heart connects with the vessels (e.g., below the pulmonic valve).
• Cardinal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins:
  • Form superior and inferior venae cavae (that connect to the right atrium (RA))
  • RCCV + RACV = SVC
  • Posterior vein + subcardinal vein + supracardinal vein = IVC IVC The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels

Cardiac Looping

• Begins in 4th week: goal is to establish left-right polarity
• Cranial end bends ventrally and caudally.
• Then, rotates over to the right (24 days)
• Atrial end shifts dorso-cranially (posteriorly and cranially) and moves to the left (35 days).
• Requires cilia and dynein involvement
• Defect in dynein function → dextrocardia (heart on the right side, seen in Kartagener’s syndrome ( primary ciliary dyskinesia Primary Ciliary Dyskinesia Primary ciliary dyskinesia (PCD), also known as immotile-cilia syndrome, is an autosomal recessive disorder leading to an impairment that affects mucociliary clearance. Primary ciliary dyskinesia is caused by defective ciliary function in the airways and is characterized by the loss of oscillation (immotility), abnormal oscillation (dyskinesia), or absence of cilia (aplasia). Primary Ciliary Dyskinesia))

Cardiac Septation

Atrial septum

The atrial septum begins with endocardial cushions at the base of the atrial chamber and septum primum.

• Septum primum
  • Grows toward the endocardial cushions
  • Foramen (ostium) primum narrows → replaced by foramen (ostium) secundum (which forms in the septum primum as the ostium primum regresses)
  • Oxygenated blood enters RA from IVC IVC The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels → passes into left atrium (LA) (through foramen secundum) → passes into developing ventricle
  • Poorly oxygenated blood from SVC will be directed to the bulbus cordis (RV).
  • Prenatal and postnatal physiology Postnatal physiology Neonatal physiology during prenatal life differs significantly from that during postnatal life. Postnatally, the fetal circulatory system and organ systems adapt to the extrauterine environment. Placental blood supply is cut off, causing the neonate to make adaptive changes. Prenatal and Postnatal Physiology
• Septum secundum
  • Develops on the right side of septum primum
  • Foramen (ostium) secundum maintains right-to-left shunt.
  • Expands and covers most of foramen (ostium) secundum → residual opening is the foramen ovale
  • RA gets larger → pulls sinus venosus into its wall → moves SVC and IVC IVC The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels closer → one opening formed
• Foramen ovale
  • Opening between septum primum and septum secundum (shunt between right and left atria)
  • Blood continues to flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure right to left, due to ↑↑ pressure in RA
  • After birth: ↑↑ pressure in LA and decreased pressure in RA → septum primum pushed against septum secundum → foramen ovale closed
    • Usually fused shut during infancy/early childhood, but in 70%–75% of the population it remains open as a small defect ( patent foramen ovale Patent Foramen Ovale A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Patent Foramen Ovale).

Ventricular septum

• Muscular interventricular septum forms (growing from base of ventricle toward endocardial cushions).
• Aorticopulmonary septum rotates and fuses with the muscular ventricular septum to form the membranous interventricular septum (closing the interventricular foramen).
• Growth of endocardial cushions separates atria from ventricles → contributes to atrial septation and membranous portion of interventricular septum.
• Defect → membranous/muscular ventricular septal defect (VSD)
  • Most common congenital cardiac defect
  • Usually a defect in the membranous portion of the interventricular septum

Aorticopulmonary septum

• Spiral septum that divides the aorta from the pulmonary artery → forms outflow tract
• Neural crest cells migrate to truncal and bulbar ridges that spiral and fuse to form aorticopulmonary septum → forming ascending aorta and pulmonary trunk
• Also fuses with muscular portion of ventricular septum → forms membranous interventricular septum
• Defect (due to failure of migration of neural crest cells): 
  • Transposition of great vessels (TGV)
  • Tetralogy of Fallot Tetralogy of Fallot Tetralogy of Fallot is the most common cyanotic congenital heart disease. The disease is the confluence of 4 pathologic cardiac features: overriding aorta, ventricular septal defect, right ventricular outflow obstruction, and right ventricular hypertrophy. Tetralogy of Fallot
  • Persistent truncus arteriosus

Valve development

• Semilunar (aortic/pulmonic) valves: derived from endocardial cushions of outflow tract
• AV (mitral/tricuspid) valves: derived from fused endocardial cushions of AV canal
• Defects lead to stenotic, regurgitant, atretic (e.g., tricuspid atresia), or displaced (e.g., Ebstein anomaly) valves

Fetal Circulation

• Placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity brings blood through the umbilical vein (80% oxygen saturation and PO₂ of approximately 30 mm Hg)
  • Umbilical arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries have low oxygen saturation
• Ductus venosus:
  • Allows blood to bypass the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver
  • Transports blood to IVC IVC The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels from the umbilical vein
  • Blood is slightly deoxygenated due to mixing
• Pathway of oxygenated blood from IVC IVC The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels back to placenta:
  • Blood hits atrial septum → pushes the valve of the foramen ovale (2/3 to LA, 1/3 to lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs) → LA → LV → aorta → common iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries → umbilical arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries → placenta
  • Mnemonic: Remember O for Oxygenated blood as well as for Ovale.
• Pathway of deoxygenated blood from SVC: 
  • SVC → RA → RV → pulmonary trunk → ductus arteriosus → descending aorta → common iliac arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries → umbilical arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries → placenta
  • This shunt is due to high fetal pulmonary arterial resistance (partly because of low oxygen tension).
  • Mnemonic: Remember D for deoxygenated blood as well as for Ductus arteriosus and Descending aorta.
• Transition from fetal to adult circulation:
  • At birth, infant takes first breath → decreased resistance in pulmonary vasculature → increased left atrial pressure in relation to right atrial pressure, leading to the closing of the foramen ovale (becomes the fossa ovalis)
  • ↑ In oxygen (from respiration) and ↓ in prostaglandins (from placental separation) → closure of ductus arteriosus
• Fetal-postnatal derivatives:
  • Umbilical vein → ligamentum teres Ligamentum teres A cord-like remnant structure formed from the closed left fetal umbilical vein. It is located along the lower edge of the falciform ligament. Uterus, Cervix, and Fallopian Tubes hepatis ( round ligament Round ligament A fibromuscular band that attaches to the uterus and then passes along the broad ligament, out through the inguinal ring, and into the labium majus. Uterus, Cervix, and Fallopian Tubes – contained in falciform ligament)
  • Umbilical arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries → medial umbilical ligaments
  • Ductus venosus → ligamentum venosum
  • Ductus arteriosus → ligamentum arteriosum (near left recurrent laryngeal nerve)
  • Foramen ovale → Fossa ovalis

Mnemonics

1. Indomethacin helps close the patent ductus arteriosus → ligamentum arteriosum (remnant of ductus arteriosus) → remember: “Come In and close the Door!”
2. “Prostaglandins E₁ and E₂ kEEp PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA) open!”

Congenital Abnormalities

Right-to-left shunts (cyanotic lesions)

• Truncus arteriosus Truncus arteriosus Truncus arteriosus (TA) is a congenital heart defect characterized by the persistence of a common cardiac arterial trunk tract that fails to divide into the pulmonary artery and aorta during embryonic development. Truncus arteriosus is a rare congenital malformation with a high mortality rate within the 1st 5 weeks of life if not managed promptly. Truncus Arteriosus: A single large vessel arises from both ventricles due to failure of formation of the aorticopulmonary septum to divide into the pulmonary trunk and aorta. Usually, it is accompanied by a VSD. Danger of irreversible pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension (PH) or pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure. Pulmonary hypertension is grouped into 5 categories based on etiology, which include primary PAH, and PH due to cardiac disease, lung or hypoxic disease, chronic thromboembolic disease, and multifactorial or unclear etiologies. Pulmonary Hypertension. 
• TGV: Failure of the aorticopulmonary septum to spiral. Pulmonary artery arises from the LV (posterior), whereas the aorta comes out from the RV (anterior). Unsuitable for life without a shunt. In 65% of cases, TGV is accompanied by patent ductus arteriosus Patent ductus arteriosus The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA) or patent foramen ovale Patent Foramen Ovale A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Patent Foramen Ovale. In 35% of cases, it is accompanied by a ventricular septal defect. Radiologically will have an “egg on string” appearance on chest X-ray due to narrowed mediastinum Mediastinum The mediastinum is the thoracic area between the 2 pleural cavities. The mediastinum contains vital structures of the circulatory, respiratory, digestive, and nervous systems including the heart and esophagus, and major thoracic vessels. Mediastinum and Great Vessels and globular heart outline. Surgical intervention is needed, otherwise most infants die within the first few months of life.
• Tricuspid atresia: The tricuspid valve is absent, which impedes the development of the right ventricle, leading to a hypoplastic right ventricle. Requires atrial septal defect Atrial Septal Defect Atrial septal defects (ASDs) are benign acyanotic congenital heart defects characterized by an opening in the interatrial septum that causes blood to flow from the left atrium (LA) to the right atrium (RA) (left-to-right shunt). Atrial Septal Defect (ASD) and VSD for viability. Blood will flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure from the RA to the LA through the atrial septal defect Atrial Septal Defect Atrial septal defects (ASDs) are benign acyanotic congenital heart defects characterized by an opening in the interatrial septum that causes blood to flow from the left atrium (LA) to the right atrium (RA) (left-to-right shunt). Atrial Septal Defect or the patent foramen ovale Patent Foramen Ovale A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Patent Foramen Ovale. To get to the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs, blood will flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure from the RA to the LA through the patent foramen ovale Patent Foramen Ovale A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Patent Foramen Ovale, and then from the LV to the RV through the ventricular septal defect. 
• Tetralogy of Fallot Tetralogy of Fallot Tetralogy of Fallot is the most common cyanotic congenital heart disease. The disease is the confluence of 4 pathologic cardiac features: overriding aorta, ventricular septal defect, right ventricular outflow obstruction, and right ventricular hypertrophy. Tetralogy of Fallot: Most common cause of early childhood cyanosis. Accompanied by pulmonary stenosis Pulmonary stenosis Valvular disorders can arise from the pulmonary valve, located between the right ventricle (RV) and the pulmonary artery (PA). Valvular disorders are diagnosed by echocardiography. Pulmonary stenosis (PS) is valvular narrowing causing RV outflow tract obstruction. Pulmonary Stenosis, right ventricular hypertrophy, overriding aorta, and a ventricular septal defect. 
• Total anomalous pulmonary venous return (TAPVR): All pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins drain into the right heart circulation (SVC, coronary sinus, etc.). The defect is similar to the shunt from the LA to the RA. The RA and the RV cause oxygenated blood to mix with deoxygenated blood and spread throughout the body. Associated with an ASD and sometimes a PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA) to allow for right-to-left shunting to maintain cardiac output.

Mnemonic: right-to-left shunts (cyanotic lesions) (the 5 Ts):

• Truncus arteriosus: 1 vessel
• Transposition of the great vessels: 2 switched vessels
• Tricuspid atresia: 3 = tri
• Tetralogy of Fallot: 4 = tetra
• Total anomalous pulmonary venous return (TAPVR): 5 letters in the name

Left-to-right shunts (acyanotic)

• VSD: Most common congenital anomaly, associated with fetal alcohol syndrome. The defect causes communication between LV and RV. Clinical presentation is harsh, holosystolic murmur that is heard best in the tricuspid area.
• ASD: Communication between LA and RA, can lead to pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension (PH) or pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure. Pulmonary hypertension is grouped into 5 categories based on etiology, which include primary PAH, and PH due to cardiac disease, lung or hypoxic disease, chronic thromboembolic disease, and multifactorial or unclear etiologies. Pulmonary Hypertension. Clinically characterized by wide splitting of S2. There are 4 types of ASD: primum, secundum, sinus venosus, and coronary sinus, the most common being a secundum type of ASD.
• Patent ductus arteriosus ( PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA)): Normally, ductus arteriosus shunts blood from the left pulmonary artery to the aorta. This should stop after birth due to decreased levels of prostaglandin E2. Clinical presentation of PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA) is a continuous machinery-like murmur on auscultation, blue toes and normal fingers, and a widened pulse pressure. 

Other congenital abnormalities

• Coarctation of the aorta Coarctation of the aorta Coarctation of the aorta is a narrowing of the aorta between the aortic arch and the iliac bifurcation commonly around the point of insertion of the ductus arteriosus. Coarctation of the aorta is typically congenital and the clinical presentation depends on the age of the patient. Coarctation of the Aorta: The aorta narrows in the area around the ductus arteriosus to a certain point and then widens to its normal diameter. Postductal coarctation (occurring after the ductus arteriosus) is clinically silent and only present in adults. Preductal coarctation (occurring before the ductus arteriosus) is an infantile type, where clinical presentation involves cyanosis in the toes. 
• Patent foramen ovale (PFO): Present in 25% of adults. Failure of fusion of septum primum with septum secundum after increased left atrial pressure. Clinically detected with bubble test in evaluation of syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope and strokes. 
• Hypoplastic left heart syndrome: High-grade stenosis or atresia of the aortic and/or mitral valve in addition to severe hypoplasia of the left ventricle, ascending aorta, and aortic arch.
• Ebstein anomaly: Defect of the tricuspid valve, which is displaced toward the right ventricle. Tethering of septal leaflet causes tricuspid regurgitation Tricuspid regurgitation Tricuspid regurgitation (TR) is a valvular defect that allows backflow of blood from the right ventricle to the right atrium during systole. Tricuspid regurgitation can develop through a number of cardiac conditions that cause dilation of the right ventricle and tricuspid annulus. A blowing holosystolic murmur is best heard at the left lower sternal border. Tricuspid Regurgitation, which will result in right-sided heart failure. 
• Double aortic arch: Embryonic vascular malformation resulting in a double aortic arch. This can lead to subsequent constriction of the trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea and esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus.
• Endocardial cushion defect: Defect of the atrioventricular valves as well as the atrial septum and/or ventricular septum. Can present as a complete form (ASD, VSD, and severe abnormalities in the AV valves, leading to severe mixing of blood) or a partial form (only ASD and minor AV valve abnormalities). Commonly seen in patients with Down syndrome Down syndrome Down syndrome, or trisomy 21, is the most common chromosomal aberration and the most frequent genetic cause of developmental delay. Both boys and girls are affected and have characteristic craniofacial and musculoskeletal features, as well as multiple medical anomalies involving the cardiac, gastrointestinal, ocular, and auditory systems. Down Syndrome.